patch 8.2.2870: CmdlineChange event triggered twice for CTRL-R

Problem:    CmdlineChange event triggered twice for CTRL-R.
Solution:   Return CMDLINE_NOT_CHANGED from cmdline_insert_reg().
            (closes #8219)
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 4ebc341..e7d71a5 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -1253,8 +1253,11 @@
 	}
 #endif
     }
+    // remove the double quote
     redrawcmd();
-    return CMDLINE_CHANGED;
+
+    // The text has been stuffed, the command line didn't change yet.
+    return CMDLINE_NOT_CHANGED;
 }
 
 /*
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 5ed283f..bba7e72 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -1810,6 +1810,12 @@
   call feedkeys(":\<F1>\<CR>", 'xt')
   call assert_equal(['l', 'ls'], g:log)
 
+  let @b = 'b'
+  cnoremap <F1> a<C-R>b
+  let g:log = []
+  call feedkeys(":\<F1>\<CR>", 'xt')
+  call assert_equal(['a', 'ab'], g:log)
+
   unlet g:log
   cunmap <F1>
   augroup test
diff --git a/src/version.c b/src/version.c
index 0b17d91..edc95e5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2870,
+/**/
     2869,
 /**/
     2868,